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C7685.001 Resistivity controller

Resistivity Controller for Ultra-Pure Water

resistivity controller C7685 001

The C7685-001 Resistivity Controller is available for panel mouning or in a surface mounting enclosure.

C7685-001 Resistivity Controller Introduction

The C7685-001 is a special variation of our auto-ranging C7685 Conductivity Controller. The C7685-001 is designed specifically for very accurately measuring the conductivity / resistivity of ultra-pure water.

The resistivity controller can display either nS (nano-siemens) or MΩ (meg-ohms) for the measurement of ultra-pure water in industrial applications.

As temperature measurement and compensation is critical to ultra pure water applications, the C7685-001 resistivity controller uses dual slope compensation for the temperature compensation. This temperature compensation in the C7685-001 differs significantly from the temperature of other conductivity controllers in that it uses an automatic look up table for the co-efficient based on the measured conductivity value to give precise compensation in ultra-pure water applications.

The C7685-001 has built in auto-ranging to ensure that if the conductivity value increases past a set range, then the display will automatically rectify to ensure that this is visible to the operator. The range can also be set manually as required.

There are a number of control options included with the C7685-001 including 2 x On/Off control relays which correspond to two individual set-points; an alarm relay and a 4-20mA output, which is programmable and expandable.

The display is our 16 character alphanumeric LCD which gives full indication of the current conductivity / resistivity value as well as the temperature and the operating state of the relays all from the home display. The menu is easy to navigate, to ensure simple calibration and configuration of the resistivity controller.

The C7685-001 resistivity controller is designed to work with a good 2 wire conductivity cell, with or without temperature compensation, and is operated via a supply voltage of 230 / 115 VAC at 50 / 60Hz.

C7685-001 Resistivity Controller Ranges

The C7685-001 resistivity range or conductivity range of the C7685-001 is dependant upon the conductivity cell that is used. The available ranges and the granularity or resolution available at each range, is listed below. Please note:- 1000 nS = 1µS.

Cell ConstantRange 1Resolution 1Range 2Resolution 2Range 3Resolution 3Range 4Resolution 4
K=0.01 0 - 200.0nS 0.1nS 0 - 2000nS 1nS 0 - 20.00µS 0.01µS N/A N/A
K = 0.1 0 - 200.0nS 0.1nS 0 - 2000nS 1nS 0 - 20.00µS 0.01µS 0 - 200.0µS 0.1µS
K = 1.0 0 - 2000nS 1nS 0 - 20.00µS 0.01µS 0 - 200.0µS 0.1µS 0 - 2000µS 1µS
K = 10.0 0 - 20.00µS 0.01µS 0 - 200.0µS 0.1µS 0 - 2000µS 1µS 20.00mS 0.01mS

C7685-001 Resistivity Controller with Temperature Compensaton

Temperature compensation in ultra-pure water applications is absolutely critical. The C7685-001 Resistivity controller uses a sophisticated dual slope compensation where the temperature compensation is dependent upon both the measured temperature and the measured conductivity value.

The temperature compensation co-efficient is fed into the instrument using an ultra-pure water look-up table which is powered from the micro-processor, with temperature references from 10.00ºC to 25.00ºC. The temperature input may come from a conductivity cell with automatic temperature compensation or from a separate 2 / 3 wire RTD

C7685-001 Expandable 4-20mA Output

The analogue output of the C7685-001 can be configured to either 4-20mA or from 0-20mA as required. The output can be also be set proportionally or inverted to increase granularity or give proportional control to a compatible dosing pump, valve or other compatible control device.

The 4-20mA can be scaled across 2 values within a range. So for instance, in the measuring range of the 0 - 2000µS, the 20mA signal could be set at 1000µS to give an analogue current output of 12mA at 500µS.

The 4-20mA current output is isolated to 600Ω and is designed to work with control equipment, PLC's, online Data Loggers, Chart Recorders or any other device that takes an industry standard 4-20mA signal.

C7685 Resistivity Controller compatible Cell Constants

The C7685-001 resistivity controller is designed to work specifically with 2 wire conductivity cells using automatic temperature compensation.

Cell constants supported include:-

  • K=0.01 Conductivity Cells
  • K=0.1 Conductivity Cells
  • K=1.0 Conductivity Cells
  • K=10.0 Conductivity Cells

C7685-001 Resistivity Controller Set-points and Relays

The C7685-001 Resistivity Controller includes 2 x set-points which operate to individual control relays. These can be independently set to High or Low operation giving an On/Off control signal to the relay. The relays are 5 amp non inductive with a programable 0-25 second delay time on each relay.

Each set-point has an adjustable hysteresis of ±10% of the set-point value.

In addition to the control relays the C7685-001 resistivity controller includes an alarm relay which triggers when the resistivity value falls outside of the desired measurement range, with activation of a delay timer of 0-60 seconds. Alternatively the alarm relay can be set to operate form 0-60 minutes after the activation of set-point 1 or set-point 2.

C7685-001 Resistivity Controller Summary

The C7685-001 is a very accurate instrument for the measurement and control of the resistivity (or conductivity) of ultra pure water.  With measurement ranges in either conductivity nS (nano-siemens) or MΩ (MegOhms).

The C7685-001 offers unparalleled automatic temperature compensation for ultra-pure water applications and is commonly found in pharmaceutical applications, power generation and in the manufacture of semi-conductors.

C7685-001 Resistivity Controller Specifications

  • Specifications


    Model No:- C7685-001

    Conductivity Ranges (1000nS = 1µS):- 0 - 200.0nS to 0 - 20.00mS

    Supported Conductivity Cell Constants:- K=0.01, K=0.1, K=1.0, K=10.0

    Temp. Compensation:- Specific Ulta-Pure Water lookup table from base 10-25ºC

    Temp. Range:- 0ºC to 100ºC

    Set Points:- 2 Min / Max selectable, contact SPST, 5 Amp inductive

    Action:- On/Off with delay timer of 0-25 secs

    Current output:- 0-20/ 4-20mA programmable and isolated into 600Ω

    Zero:- Adjustable

    Slope:- Adjustable

    Mains Supply:- 115-230 VAC, 50 / 60Hz switch mode power supply

    Power Consumption:- 5 VA

    Weight:- 850 grams DIN version

    Dimensions:- 96 x 96 x 155mm cutout 91.5 x 91.5mm

  • Features


    • Panel mounting auto-ranging conductivity controller.
    • Precision Conductivity monitoring for process and effluent applications
    • Easy to setup, install and use
    • Full 16 character alphanumeric display showing full soltuion parameters on the home screen and currnet relay states..
    • Two control relays and an alarm relay with easy to configure set-points.
    • Programmable 4-20mA output which is isolated into 600Ω - ideal for connecting to control equipment, PLC's, online data loggers or digital chart recorders.
    • Compatible with a huge range of 2-wire conductivity cells, 4 wire conductivity cells, and toroidal or inductive conductivity cells with a micro-transmitter.
  • Data Sheets

    Data Sheets


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